Non-volatile resistance variable devices

ABSTRACT

A chalcogenide comprising material is formed to a first thickness over the first conductive electrode material. The chalcogenide material comprises A x B y . A metal comprising layer is formed to a second thickness over the chalcogenide material. The metal comprising layer defines some metal comprising layer transition thickness for the first thickness of the chalcogenide comprising material such that when said transition thickness is met or exceeded, said metal comprising layer when diffused within said chalcogenide comprising material transforms said chalcogenide comprising material from an amorphous state to a crystalline state. The second thickness being less than but not within 10% of said transition thickness. The metal is irradiated effective to break a chalcogenide bond of the chalcogenide material at an interface of the metal and chalcogenide material and diffuse at least some of the metal into the chalcogenide material.

This application is a divisional of U.S. application Ser. No.09/943,190, filed on Aug. 29, 2001, which is herein incorporated byreference in its entirety.

TECHNICAL FIELD

This invention relates to non-volatile resistance variable devices, tomethods of forming a programmable memory cell of memory circuitry and tonon-volatile resistance variable devices.

BACKGROUND OF THE INVENTION

Semiconductor fabrication continues to strive to make individualelectronic components smaller and smaller, resulting in ever denserintegrated circuitry. One type of integrated circuitry comprises memorycircuitry where information is stored in the form of binary data. Thecircuitry can be fabricated such that the data is volatile ornon-volatile. Volatile storing memory devices result in loss of datawhen power is interrupted. Non-volatile memory circuitry retains thestored data even when power is interrupted.

This invention was principally motivated in making improvements to thedesign and operation of memory circuitry disclosed in the Kozicki et al.U.S. Pat. Nos. 5,761,115; 5,896,312; 5,914,893; and 6,084,796, whichultimately resulted from U.S. patent application Ser. No. 08/652,706,filed on May 30, 1996, disclosing what is referred to as a programmablemetallization cell. Such a cell includes opposing electrodes having aninsulating dielectric material received therebetween. Received withinthe dielectric material is a fast ion conductor material. The resistanceof such material can be changed between highly insulative and highlyconductive states. In its normal high resistive state, to perform awrite operation, a voltage potential is applied to a certain one of theelectrodes, with the other of the electrode being held at zero voltageor ground. The electrode having the voltage applied thereto functions asan anode, while the electrode held at zero or ground functions as acathode. The nature of the fast ion conductor material is such that itundergoes a structural change at a certain applied voltage. With suchvoltage applied, a single conductive dendrite or filament extendsbetween the electrodes, effectively interconnecting the top and bottomelectrodes to electrically short them together.

Once this occurs, dendrite growth stops, and is retained when thevoltage potentials are removed. Such can effectively result in theresistance of the mass of fast ion conductor material between electrodesdropping by a factor of 1,000. Such material can be returned to itshighly resistive state by reversing the voltage potential between theanode and cathode, whereby the filament disappears. Again, the highlyresistive state is maintained once the reverse voltage potentials areremoved. Accordingly, such a device can, for example, function as aprogrammable memory cell of memory circuitry.

The preferred resistance variable material received between theelectrodes typically and preferably comprises a chalcogenide materialhaving metal ions diffused therein. A specific example is germaniumselenide having silver ions diffused therein. The present method ofproviding the silver ions within the germanium selenide material is toinitially chemical vapor deposit the germanium selenide glass withoutany silver being received therein. A thin layer of silver is thereafterdeposited upon the glass, for example by sputtering, physical vapordeposition or other technique. An exemplary thickness is 200 Angstromsor less. The layer of silver is irradiated, preferably withelectromagnetic energy at a wavelength less than 500 nanometers. Thethin nature of the deposited silver enables such energy to pass throughthe silver to the silver/glass interface effective to break achalcogenide bond of the chalcogenide material. This may form Ag₂Se,which effectively dopes the glass with silver.

Saturation of silver in germanium selenide is apparently at a maximum ofabout 34 atomic percent or less depending on the germanium selenidestoichiometry. Yet, preferred existing technology for cell fabricationconstitutes a concentration which is less than the maximum; in the caseof 34 atomic percent maximum, an example concentration would be about 27atomic percent.

After the chalcogenide material is provided with silver to a desiredconcentration, the top electrode material (typically silver) is nextdeposited. But, as the silver doping/diffusion into the chalcogenidematerial approaches the maximum or saturation, some Ag₂Se was discoveredto form at the surface and remain there as opposed to diffusing into theglass. Further, the surface Ag₂Se was typically in the form ofsemicircular nodules or bumps anywhere from 50 Angstroms to 20 micronsacross. Unfortunately when the typical silver electrode material issubsequently deposited, such tends to mound on top of these previousbumps. This can create voids to the doped germanium glass through thetop electrode material, whereby the silver doped germanium selenideglass is partially exposed. Unfortunately, some of the photodevelopersolutions typically used for patterning the top electrode (i.e.tetramethyl ammonium hydroxide) will etch the glass that is exposed.

It would be desirable to overcome or at least reduce this problem. Whilethe invention was principally motivated in overcoming this problem, itis in no way so limited. The artisan will appreciate applicability ofthe invention in other aspects unrelated to the problem, with theinvention only being limited by the accompanying claims as literallyworded and as appropriately interpreted in accordance with the doctrineof equivalents.

SUMMARY

The invention includes non-volatile resistance variable devices, methodsof forming a programmable memory cell of memory circuitry andnon-volatile resistance variable devices. In one implementation, amethod of forming a non-volatile resistance variable device includesforming a first conductive electrode material on a substrate. Anamorphous chalcogenide comprising material is formed to a firstthickness over the first conductive electrode material. The chalcogenidematerial comprises A_(x)B_(y), where “B” is selected from the groupconsisting of S, Se and Te and mixtures thereof, and where “A” comprisesat least one element which is selected from Group 13, Group 14, Group15, or Group 17 of the periodic table. A metal comprising layer isformed to a second thickness over the chalcogenide material. The metalcomprising layer defines or has some metal comprising layer transitionthickness for the first thickness of the chalcogenide comprisingmaterial such that when said transition thickness is met or exceeded,said metal comprising layer when diffused within said chalcogenidecomprising material transforms said chalcogenide comprising materialfrom an amorphous state to a crystalline state. Yet, the secondthickness is less than but not within 10% of said transition thickness.The metal is irradiated effective to break a chalcogenide bond of thechalcogenide material at an interface of the metal and chalcogenidematerial and diffuse at least some of the metal into the chalcogenidematerial, and said chalcogenide comprising material remains amorphousafter the irradiating. After the irradiating, a second conductiveelectrode material is deposited over the chalcogenide material, andwhich is continuous and completely covering at least over thechalcogenide material. The second conductive electrode material isformed into an electrode of the device.

In one implementation, a metal comprising layer is formed to a secondthickness less than the first thickness over the chalcogenide comprisingmaterial. The metal is irradiated effective to break a chalcogenide bondof the chalcogenide material at an interface of the metal andchalcogenide comprising material and at least some of the metal isdiffused into the chalcogenide comprising material, and saidchalcogenide comprising material remains amorphous after theirradiating. The chalcogenide comprising material after the irradiatinghas a first region which is displaced from the interface at least by aninterface region having a higher content of “A” than the first region.After the irradiating, a second electrode material is formed operativelyproximate the chalcogenide material.

Other implementations and aspects are contemplated and disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic sectional view of a semiconductor waferfragment in process in accordance with an aspect of the invention.

FIG. 2 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that shown by FIG. 1.

FIG. 3 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that shown by FIG. 2.

FIG. 4 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that shown by FIG. 3.

FIG. 5 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that shown by FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

Referring to FIG. 1, a semiconductor wafer fragment 10 is shown in butone preferred embodiment of a method of forming a non-volatileresistance variable device. By way of example only, example such devicesinclude programmable metallization cells and programmable opticalelements of the patents referred to above, further by way of exampleonly, including programmable capacitance elements, programmableresistance elements, programmable antifuses of integrated circuitry andprogrammable memory cells of memory circuitry. The above patents areherein incorporated by reference. The invention contemplates thefabrication techniques and structure of any existing non-volatileresistance variable device, as well as yet-to-be developed such devices.In the context of this document, the term “semiconductor substrate” or“semiconductive substrate” is defined to mean any constructioncomprising semiconductive material, including, but not limited to, bulksemiconductive materials such as a semiconductive wafer (either alone orin assemblies comprising other materials thereon), and semiconductivematerial layers (either alone or in assemblies comprising othermaterials). The term “substrate” refers to any supporting structure,including, but not limited to, the semiconductive substrates describedabove. Also in the context of this document, the term “layer”encompasses both the singular and the plural unless otherwise indicated.Further, it will be appreciated by the artisan that “resistance variabledevice” includes devices wherein a property or properties in addition toresistance is/are also varied. For example, and by way of example only,the device's capacitance and/or inductance might also be changed inaddition to resistance.

Semiconductor wafer fragment 10 comprises a bulk monocrystallinesemiconductive material 12, for example silicon, having an insulativedielectric layer 14, for example silicon dioxide, formed thereover. Afirst conductive electrode material 16 is formed over dielectric layer14. By way of example only, preferred materials include any of thosedescribed in the incorporated Kozicki et al. patents referred to abovein conjunction with the preferred type of device being fabricated. Adielectric layer 18 is formed over first electrode material 16. Siliconnitride is a preferred example.

An opening 20 is formed through layer 18 to conductive electrode layer16. Such is filled with an amorphous chalcogenide comprising material 22to a first thickness, which in this example is essentially defined bythe thickness of layer 18. By way of example only, an exemplary firstthickness range is from 100 Angstroms to 1000 Angstroms. Thechalcogenide comprising material comprises A_(x)B_(y), where “B” isselected from the group consisting of S, Se and Te and mixtures thereof,and where “A” comprises at least one element which is selected fromGroup 13 (B, Al, Ga, In, Tl), Group 14 (C, Si, Ge, Sn, Pb), Group 15 (N,P, As, Sb, Bi), or Group 17 (F, Cl, Br, I, At) of the periodic table. Byway of example only, preferred elements for “A” are Ge and Si. Anexample preferred method of forming material 22 over substrate 10 is bychemical vapor deposition to completely fill opening 20, followed by aplanarization technique, for example chemical mechanical polishing.Material 22 is preferably formed to be amorphous and remains amorphousin the finished device.

A metal comprising layer 24 is formed to a second thickness overchalcogenide material 22. Exemplary metals, by way of example only,include silver, zinc and copper. In one embodiment, the second thicknessis less than but not within 10% of a “transition thickness”.Specifically, the material of the metal comprising layer defines or hassome transition thickness for a given thickness of the chalcogenidematerial such that when said material transition thickness is met orexceeded, the metal comprising layer when diffused within saidchalcogenide comprising material transforms said chalcogenide comprisingmaterial from an amorphous state to a crystalline state. Such transitionthickness can be different for different stoichiometry chalcogenidematerials and for different metals. Further, the second thickness isbelow but not within 50% of the transition thickness in one preferredembodiment, not within 65% in another preferred embodiment, and notwithin 85% in yet another preferred embodiment.

For example, and by way of example only, a metal layer consistingessentially of elemental silver received over a 500 Angstrom germaniumselenide glass having 25% atomic germanium and 75% atomic selenide has atransition thickness of 140 Angstroms. Accordingly in one preferredembodiment in such example, a metal layer 24 consisting essentially ofelemental silver will have a thickness less than 124 Angstroms (i.e.,not within 10%), in another embodiment a thickness less than 70Angstroms (i.e., not within 50%), in another embodiment a thickness lessthan 49 Angstroms (i.e., not within 65%), and in another embodiment athickness less than 21 Angstroms (i.e., not within 85%).

Referring to FIG. 2, metal 24 is irradiated effective to break achalcogenide bond of the chalcogenide material at an interface of metal24 and chalcogenide material 22, and diffuse at least some of metal 24into chalcogenide material 22, with chalcogenide comprising material 22remaining in the amorphous state after the irradiating. In FIG. 2,material 22 is designated with numeral 23 and peppered in the drawingsto indicate metal ions being received therein. A preferred irradiatingincludes exposure to actinic radiation having a wavelength from about164–904 nanometers, with radiation exposure at between 404–408nanometers being a more specific example. A more specific example is aflood UV exposure tool operating at 4.5 milliwatts/cm² energy for 15minutes in an oxygen-containing ambient at room temperature andpressure. A mechanism of incorporation might include Ag₂Se formation atthe chalcogenide surface/interface, and diffusion doping thereof intomaterial 22.

All of material 24 received directly over chalcogenide comprisingmaterial 22 might be diffused to within such material as shown, or onlysome portion thereof might. The thickness of layer 24 is also chosen tobe suitably thin to enable the impinging electromagnetic radiation toessentially transparently pass through material 24 to the interface ofsuch material with chalcogenide material 22. The exemplary preferredthickness is as described above in comparison with the thickness ofchalcogenide material 22, and is preferably less than or equal to 200Angstroms.

The apparent linear thickness of layer 24 as a percentage of the linearthickness of chalcogenide material 22 effectively results in the sameapproximate metal incorporation in atomic percent within thechalcogenide material. In other words, a 2% to 20% thick metal layercompared to that of the underlying chalcogenide material will result inmetal incorporation of an atomic percent of from about 2% to about 20%respectively. Accordingly as compared to conventional prior art, a loweratomic percent incorporation is conducted to within the chalcogenidematerial, and has been discovered in preferred embodiments to result inthe elimination of surface agglomeration of Ag₂Se which is understood tohave principally caused the discontinuous subsequent electrode formationof the prior art. Thereby in the preferred embodiment, a continuous,void-free, complete covering of a subsequently deposited electrode layerwas achieved in connection with deposition over at least chalcogenidematerial 23, as further described below.

In one exemplary embodiment, layer 24 of metal is formed to a secondthickness over the chalcogenide material and the irradiating iseffective to produce the chalcogenide material 23 (FIG. 2) to have aninterface region 25 and a first region 23 which is displaced from theinterface of the metal and chalcogenide material by interface region 25.In this exemplary embodiment, interface region 25 is characterized by ahigher content of “A” of the A_(x)B_(y) material as compared to thecontent of “A” in first region 23. Apparently, photodoping or otherirradiation doping to the stated lower second thicknesses can result ingreater driving of silver or other metal into germanium selenide orother glasses which can result in an outer germanium rich layer of theglass. This may facilitate a preferred lack of surface agglomeration ofAg₂Se.

Interface region 25 is preferably formed to have a thickness of lessthan or equal to 100 Angstroms. Further, such is preferably formed tohave a thickness of at least 10 Angstroms. Further preferably, interfaceregion 25 and first region 23 are formed to have substantially the sameconcentration of the diffused metal. Further preferably, interfaceregion 25 and first region 23 are respectively homogenous.

Referring to FIG. 3, after the irradiating, a second conductiveelectrode material 26 is deposited over chalcogenide material 23. In thepreferred embodiment, such second conductive electrode material iscontinuous and completely covers at least over chalcogenide material 23.An example preferred thickness range for second electrode material layer26 is from 140 Angstroms to 200 Angstroms. The first and secondconductive electrode materials might be the same material(s), ordifferent material(s). By way of example only, preferred top and bottomelectrode materials include silver, tungsten, platinum, nickel, carbon,chromium, molybdenum, aluminum, magnesium, copper, cobalt, palladium,vanadium, titanium, alloys thereof and compounds including one or moreof these elements. In accordance with a preferred programmablemetallization cell embodiment, and where “A” is Ge, at least one ofmaterials 16 and 26 comprises silver. During formation of layer 26, someof it might diffuse into layer 23. Layer 26 and any remnant material 24received directly over chalcogenide material 23 will constitute oneelectrode of the resistance variable device being fabricated, with layer16 constituting another or second electrode for the device.

Referring to FIG. 4, materials 24 and 26 are patterned into an electrode30. Patterning to produce electrode 30 is typically and preferablyconducted utilizing photolithography. Such provides but one preferredexample of forming a second electrode material operatively proximate thechalcogenide material. In a preferred embodiment, such results in theformation of a non-volatile resistance variable device which isfabricated into a programmable memory cell of memory circuitry. In onepreferred embodiment, the device is finally formed to have aconcentration of metal in chalcogenide material 23 of less than 30%atomic in a lowest of a plurality of variable resistance states.

Referring to FIG. 5, one or more dielectric layers 32 are ultimatelyformed over the device. Of course, intervening conductive andsemiconductive layers might also be provided to form other lines anddevices outwardly of the depicted device.

Independent of the method of fabrication, the invention comprises anon-volatile resistance variable device comprising some substrate havinga first electrode formed thereover, for example electrode 16. Aresistance variable chalcogenide material 23 having metal ions diffusedtherein is received operatively adjacent the first electrode. A secondelectrode, for example electrode 30, is received operatively adjacentthe resistance variable chalcogenide material. The chalcogenide materialcomprises A_(x)B_(y), where “B” is selected from the group consisting ofS, Se and Te and mixtures thereof, and where “A” comprises at least oneelement which is selected from Group 13, Group 14, Group 15, or Group 17of the periodic table.

The second electrode and resistance variable chalcogenide materialoperatively connect at an interface. The chalcogenide material has afirst region 23 which is displaced from the interface at least by achalcogenide material interface region 25 having a higher content of “A”than first region 23. Preferably and as shown, first region 23 extendsto first electrode 16.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A resistance variable device comprising: a substrate having a firstelectrode formed thereover; a resistance variable chalcogenidecomprising material having metal ions diffused therein receivedoperatively adjacent the first electrode, the chalcogenide materialcomprising A_(x)B_(y), where “B” is selected from the group consistingof S, Se and Te and mixtures thereof, and where “A” comprises at leastone element which is selected from Group 13, Group 14, Group 15, orGroup 17 of the periodic table; a second electrode received operativelyadjacent the resistance variable chalcogenide comprising material; andthe second electrode and resistance variable chalcogenide comprisingmaterial operatively connecting at an interface, the chalcogenidecomprising material having a first region which is displaced from theinterface at least by a chalcogenide material interface region having ahigher content of “A” than the first region, and no metal chalcogenideagglomerations at the interface.
 2. The device of claim 1 wherein “A”comprises Ge or Si.
 3. The device of claim 1 wherein “A” comprises Ge.4. The device of claim 1 wherein “A” comprises Ge, and “B” comprises Se.5. The device of claim 1 wherein “A” comprises Ge, “B” comprises Se, andthe metal ions comprise Ag.
 6. The device of claim 1 wherein theinterface region has a thickness of less than or equal to 100 Angstroms.7. The device of claim 1 wherein the interface region has a thickness ofgreater than or equal to 10 Angstroms.
 8. The device of claim 1 whereinthe interface region has a thickness of less than or equal to 100Angstroms and greater than or equal to 10 Angstroms.
 9. The device ofclaim 1 wherein the interface region is substantially homogenous. 10.The device of claim 1 wherein the interface and first regions havesubstantially the same concentration of the metal.
 11. The device ofclaim 1 wherein the interface region is substantially homogenous, andthe interface and first regions have substantially the sameconcentration of the metal.
 12. The device of claim 1 wherein the secondelectrode material predominately comprises elemental silver.
 13. Aresistance variable device comprising: a substrate having a firstelectrode formed thereover; a resistance variable chalcogenidecomprising material having silver ions diffused therein receivedoperatively adjacent the first electrode, the chalcogenide materialcomprising Ge_(x)Se_(y), wherein the atomic percent of silver within theresistance variable chalcogenide comprising material is approximately 20percent or less; a second electrode received operatively adjacent theresistance variable chalcogenide comprising material; and the secondelectrode and resistance variable chalcogenide comprising materialoperatively connecting at an interface, the chalcogenide comprisingmaterial having a first region which is displaced from the interface atleast by a chalcogenide material interface region having a highercontent of Ge than the first region, and no silver chalcogenideagglomerations at the interface.
 14. A resistance variable devicecomprising: a substrate having a first electrode formed thereover; aresistance variable chalcogenide comprising material having silver ionsdiffused therein received operatively adjacent the first electrode, thechalcogenide material comprising Ge_(x)Se_(y), wherein the resistancevariable chalcogenide comprising material is not saturated with silverions; a second electrode received operatively adjacent the resistancevariable chalcogenide comprising material; and the second electrode andresistance variable chalcogenide comprising material operativelyconnecting at an interface, the chalcogenide comprising material havinga first region which is displaced from the interface at least by achalcogenide material interface region having a higher content of Gethan the first region, and no silver chalcogenide agglomerations at theinterface.